In general, an electric motor vehicle is configured to capture electric power from an overhead wire with a current collector and drive, using the captured electric power, an electric motor with a power converting apparatus such as an inverter to travel.
In the electric motor vehicle, when the vehicle is braked, a so-called regenerative brake for regeneratively operating the electric motor to obtain braking force is used. Regenerated power generated at this point is supplied to loads such as other power running vehicles present near the own vehicle and an air conditioner of the vehicle via the overhead wire, a third rail, or the like and consumed in the loads.
However, in the early morning, at night, and a quiet railroad section where the number of trains in operation is small, in some case, no other vehicles are present near the own vehicle (regenerative loads are insufficient) and the regenerated power generated by the regenerative brake is not sufficiently consumed. When the regenerated power of the own vehicle is larger than power consumed by other vehicles, an overhead wire voltage rises. It is likely that various apparatuses connected to the overhead wire are tripped by an excess voltage or broken.
Therefore, when the overhead wire voltage rises, an inverter apparatus perform regeneration reducing control for reducing a regenerative brake and suppressing generation of regenerated power. When the regeneration reducing control is performed, because regenerative braking force is reduced by the regeneration reducing control, the reduced and insufficient braking force is supplemented by a frictional brake.
On the other hand, the use of the friction brake leads to discarding a part of kinetic energy of an electric motor vehicle in the atmosphere that can originally perform power regeneration. Therefore, there is a problem from the viewpoint of energy saving.
Therefore, a system is developed in which a power storage element such as a secondary battery or an electric double layer capacitor is mounted on an electric motor vehicle and regenerated power is stored in the power storage element according to necessity to obtain a stable regenerative brake even if regenerative loads are insufficient. Because the electric power stored in the power storage element can be used when the electric motor vehicle is accelerated next time, energy saving is realized.
When the electric motor vehicle mounted with the power storage element travels in a non-electrified section where electricity reception from an overhead wire is not performed, an electric motor is driven and accelerated using only the electric power from the power storage element. All regenerated power generated by the electric motor during braking is stored in the power storage element.